1. Field of the Invention
The ability to introduce genetic material into a functioning cell, where the genetic material is then expressed, has opened up a phantasmorgia of opportunities. With each new discovery of the manner in which the replication and expression of genetic material is naturally controlled, there is an ever increasing capability of modifying cells to desired useful ends.
Much of the original work with hybrid DNA technology concerned prokaryotic organisms. For the most part, molecular biology has looked to prokaryotic organisms for an understanding of genetic control of cell growth and proliferation. However, for many purposes, it will be desirable or necessary to transform eukaryotic cells. Much less is known of the manner of genetic replication and regulation in eukaryotic cells. One distinct difference between eukaryotes and prokaryotes for the purposes of hybrid DNA technology is the substantial absence in most eukaryotes of plasmids or other extrachromosomal DNA.
In transforming a cell, it is not sufficient that an individual cell accept the genetic material. It is also necessary that upon mitosis, the progency cell have retained the introduced genetic material. In order for this to occur, at each mitotic event, the introduced genetic material must be replicated and upon division, one copy be retained by each cell. Therefore, when introducing genetic material into a eukaryotic cell, means must be provided involving the coding which provides for replication of the genetic material and stable maintenance upon mitosis.
2. Description of the Prior Art
The following references concern autonomously replicating segments and centromeres: Kingsman et al., Gene, 7 (1979) 141-152; Hsiao and Carbon, Proc. Natl. Acad. Sci. USA 76, 3829-3833 (1979); Clarke and Carbon, ibid 77, 2173-2177 (1980) (Note particularly, Note added in proof, on page 2177) and an Abstract at the Alfred Benzon Symposium, June, 1980, Copenhagen, Denmark. Also note the reference cited in the aforestated references, particularly Hinnen et al., Proc. Natl. Acad. Sci. USA 75, 1929-1933 (1978) and Struhl et al., ibid 76 1035-1039 (1979).